This invention relates to a method of determining completeness of sterilization and aeration cycle in an ethylene oxide sterilizing process by the use of an indicator. Ethylene oxide sterilizing systems are well known in the art and are widely used in the hospitals and laboratories for destruction of microorganisms. Briefly in ethylene oxide sterilization, goods to be sterilized such as surgical instruments, rubber, and plastic devices, etc., are placed inside the sterilizing chamber and exposed for a period to ethylene oxide under controlled humidity and temperature conditions. The period cycles are usually timed to last 1 1/2 hours to 4 hours depending upon the nature of articles being sterilized. After sterilization goods are placed in an aerator to dispel ethylene oxide. The validity of such sterilizing cycle is often determined by chemical indicators in hospital practice. Indicators used presently show the presence of ethylene oxide by a color change. A compound proposed for use as an exposure indicator for ethylene oxide sterilization has been described in the literature. Brewer and Arnsberger in Journal of Pharmaceutical Sciences, Vol. 55, No. 1, January 1966 pages 57-59, disclose that 4(4'-nitrobenzyl) pyridine reacts with ethylene oxide to form a dye which is blue in alkaline medium. Although this indicator has a high degree of specificity to ethylene oxide, the fact that it is too highly sensitive to this alkylating agent limits its utility to that of an exposure indicator, indicating merely that the material being treated has been exposed to ethylene oxide. In order to determine whether the extent of exposure to the alkylating agent has been sufficient to render sterility to the material being treated, it is necessary to rely upon the use of positive spore controls and then assay the effectiveness of kill, a procedure which has the disadvantage of being rather inconvenient and time consuming. Furthermore, the color change exhibited by this exposure indicator is inhibited by the presence of carbon dioxide, the principal inert diluent gas commonly employed with ethylene oxide. Attempts have been made to correct this problem. In U.S. Pat. No. 3,627,469 substituted pyridines quinolines or isoquinolines are suggested as indicators. However, their use is limited to sterilization process. They cannot be used to monitor aeration process.
Indicators monitoring dissipation of ethylene oxide are available and one such device is disclosed in U.S. Pat. No. 3,738,811, this device is not a true telltale indicator. The method according to this patent calls for frequent rupturing of an ampule and the moment of rupturing is merely a guess work. An accurate indication of aerating cycle is essential. Some intricate surgical instruments and medical devices if not completely aerated may still contain ethylene oxide and if used may be hazardous to patients and trigger malpractice suits against hospitals.
We have found that the problems associated with the use of 4-(4'nitrobenzyl) pyridine can be obviated by desensitizing it with additives. The proposed telltale indicator as described in this invention changes its color from white to violet during a sterilizing cycle and the same indicator remaining with the sterilized goods in the aerator indicates the completion of that cycle by a change of color from violet to gray green. No indicators are known in the prior art which show the completion of total ethylene oxide cycle, namely exposure to ethylene oxide as well as aeration, by a color change. This invention eliminates the need of two separate indicators.